Embodiments of the present invention relate to a process for preparing monochloroethylene carbonate from ethylene carbonate, as well as to a process comprising the further conversion of the monochloroethylene carbonate to vinylene carbonate.
Vinylene carbonate is an important intermediate for the synthesis of pharmaceuticals, plant protection agents, polymers, especially for lacquers, and various other chemicals. One important use of vinylene carbonate is as an additive to solutions for batteries, especially for lithium ion batteries. Lithium ion batteries are, for example, used as storage batteries in hybrid electric vehicles.
Generally, vinylene carbonate is prepared from monochloroethylene carbonate by eliminating hydrogen chloride by means of a tertiary amine, usually triethylamine, in an organic solvent. The monochloroethylene carbonate used as a starting material in this elimination reaction is prepared by radical chlorination of ethylene carbonate. Examples of chlorination agents include sulfuryl chloride in combination with a radical initiator, or chlorine gas under the irradiation of UV light. Hydrogen chloride inevitably evolving as a by-product favors the formation of unwanted chlorinated decomposition products of ethylene carbonate. These unwanted chlorinated decomposition products present in the monochloroethylene carbonate which is—for economical reasons—usually directly employed in the synthesis of vinylene carbonate without any purification result in impurities of the final vinylene carbonate product which are difficult to remove. Consequently, a time-consuming and thus expensive recrystallization step is necessary in addition to several distillation steps in order to obtain vinylene carbonate having a high purity, e.g., required for battery applications.
JP-A-2007091604 describes a method for producing monochloroethylene carbonate comprising reacting ethylene carbonate with chlorine gas under the irradiation of light, wherein the chlorine gas is mixed with an inert gas and the gas mixture is then introduced into the reaction system. The method is said to improve the purity of the monochloroethylene carbonate product. However, the purity may still be insufficient for some uses.